A matrix camera includes a sensor with a surface made up of light sensitive pixels arranged in a two-dimensional array, for example including many lines of many pixels in each line. Thus, at any given moment, the sensor array can capture an image of an entire object, for example, if the entire object is imaged to fall completely onto the array. On the other hand, a line camera has a sensor that only has, for example, a single line of light sensitive pixels. A two-line camera has a sensor with two lines of light sensitive pixels. Thus, a single-line camera or two-line camera typically cannot simultaneously at one moment capture a complete image of the entire object to be imaged, but rather at any moment captures only a single line or two lines of pixels of an image of one or two lines of the object. The complete image of the entire object that is to be imaged is obtained only by the motion of the object relative to the camera, so that the one or two lines of light sensitive pixels can successively image or capture successive lines of the object until all of the lines of the object have been imaged in time succession. Typically, the motion of the object relative to the camera involves an orthogonal motion of the camera relative to the object or of the object relative to the camera. It is not significant whether the camera moves or the object moves or both the camera and the object move. Only the relative motion between the two is important.
Line cameras are often used for monitoring industrial production processes. In many cases of such industrial production monitoring, the object to be imaged is moved by means of a conveyor belt under a fixed or rigidly installed camera. For example, the objects on the conveyor belt are products being manufactured, which products are to be monitored for possible defects, damage, or failure to meet specifications, during the manufacturing process. For this purpose, pictures or images of the objects are produced by the line camera as the objects move through the field of view of the camera. The image data are automatically analyzed in a digital image processing arrangement connected to the camera. On the basis of this analysis, reject products, e.g. products with defects or damage, or products that fail to meet the required specifications, can be identified and sorted out of the production process.
In order to be able to correctly assemble the individual lines of image data generated by a line camera to produce a complete image of the object, and to be able to correctly interpret and evaluate the image, it is necessary to recognize the relative direction of motion of the camera and the object relative to one another. This is especially pertinent in the application of line cameras in so-called machine vision systems, in which various different relative motion directions and varying or changing motion directions can arise. In that regard, a line camera having exactly only one line of light sensitive pixels is conventionally known, whereby this camera is optimized for a bi-directional operation. A significant disadvantage of such a single line camera, however, is that the relative direction of motion cannot be determined solely from the acquired image data alone. Rather, in each case, either an additional sensor is necessary, or the human user of the system must input direction information in order to enable the relative direction of motion, and a possible change of the relative direction of motion, to be taken into consideration in the image processing. A further disadvantage of single line cameras is that they cannot provide redundant image data from the same single moment or point in time. Instead, only a single line of the object can be imaged at any given single point in time. While successive image points or lines can be recorded successively with successive time offsets, it is not possible to carry out a comparison of image data that were simultaneously recorded from spatially different parts of the object.
In this context, the image processing concept and term “optical flow” is also known. This term refers to a vector field that is produced in various optical technical methods, and that specifies the two-dimensional direction of motion and velocity of each image point or each pixel of an image sequence. Processing the data for the vector field is complicated and relatively computationally costly and time-consuming.